drm/amd/display: Underflow Seen on DCN401 eGPU

[WHY]
In dcn401 we read clock values before FW is loaded. These incorrect
values cause the driver to believe that we are running higher clocks
than what we actually have. This then causes corruption/underflow for
the eGPU.

[HOW]
When new values are read from HW, update internal structures to
propagate the new/correct value. Fixes issue
Signed-off-by: Daniel Sa <Daniel.Sa@amd.com>
Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/hwss/dcn401/dcn401_hwseq.c

@@ -221,6 +221,7 @@ void dcn401_init_hw(struct dc *dc)
 	int edp_num;
 	uint32_t backlight = MAX_BACKLIGHT_LEVEL;
 	uint32_t user_level = MAX_BACKLIGHT_LEVEL;
+	int current_dchub_ref_freq = 0;
 
 	if (dc->clk_mgr && dc->clk_mgr->funcs && dc->clk_mgr->funcs->init_clocks) {
 		dc->clk_mgr->funcs->init_clocks(dc->clk_mgr);
@@ -264,6 +265,8 @@ void dcn401_init_hw(struct dc *dc)
 					dc->ctx->dc_bios->fw_info.pll_info.crystal_frequency,
 					&res_pool->ref_clocks.dccg_ref_clock_inKhz);
 
+			current_dchub_ref_freq = res_pool->ref_clocks.dchub_ref_clock_inKhz / 1000;
+
 			(res_pool->hubbub->funcs->get_dchub_ref_freq)(res_pool->hubbub,
 					res_pool->ref_clocks.dccg_ref_clock_inKhz,
 					&res_pool->ref_clocks.dchub_ref_clock_inKhz);
@@ -433,8 +436,9 @@ void dcn401_init_hw(struct dc *dc)
 		dc->caps.dmub_caps.mclk_sw = dc->ctx->dmub_srv->dmub->feature_caps.fw_assisted_mclk_switch_ver > 0;
 		dc->caps.dmub_caps.fams_ver = dc->ctx->dmub_srv->dmub->feature_caps.fw_assisted_mclk_switch_ver;
 		dc->debug.fams2_config.bits.enable &= dc->ctx->dmub_srv->dmub->feature_caps.fw_assisted_mclk_switch_ver == 2;
-		if (!dc->debug.fams2_config.bits.enable && dc->res_pool->funcs->update_bw_bounding_box) {
-			/* update bounding box if FAMS2 disabled */
+		if ((!dc->debug.fams2_config.bits.enable && dc->res_pool->funcs->update_bw_bounding_box)
+			|| res_pool->ref_clocks.dchub_ref_clock_inKhz / 1000 != current_dchub_ref_freq) {
+			/* update bounding box if FAMS2 disabled, or if dchub clk has changed */
 			if (dc->clk_mgr)
 				dc->res_pool->funcs->update_bw_bounding_box(dc,
 									    dc->clk_mgr->bw_params);